How do I solve for the specific heat in a heat transfer problem?

In summary: But, doing it this way will be more difficult to understand, and could lead to confusion in the future. For now, I think it's easier just to think of them as being equal.
  • #1
mathzeroh
98
0
how're all the fine scientists feeling today?

well i jst had a question regarding my specific heat & Co. homework.

ok here it is: "When a 25g block of metal alloy at 215 degrees celcius (i don't know how to make that round degree symbol on here) is dropped into 85g of water at 22 deg.C, the final temperature is 37 deg.C. What is the specific heat of the alloy?

i worked it out 2 different times and got 2 different answers each time. :cry: :rolleyes:
once i got 15 J/(g*degrees Celcius) and then the second time i got 1.2 J/(g*degrees Celcius)

any help at all appreciated! thanks in advance!
 
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  • #2
Okay.I don't use sign conventions for given and received heat,so i'll simply write

[tex] Q_{\mbox{given}}=m_{\mbox{alloy}}c_{\mbox{alloy}}(215-37) [/tex]

[tex] Q_{\mbox{received}}=m_{\mbox{water}}c_{\mbox{water}}(37-22) [/tex]

Set the 2 #-s equal and then solve for the unknown.

Daniel.

P.S.Pay attention with the units.I'd advise u to use SI-mKgs.
 
  • #3
wouldnt it be (37-215) because delta T is always t final minus t initial??

and what did you mean by SI-mKgs ? :confused:
 
  • #4
Nope,i don't use convention signs.The heats are always positive and equal...(in this 2 body thermal interraction).

SI-mKgs from Système International-metre,Kilogramme,sécond .

Daniel.
 
  • #5
oh.

well when heat is negative, it meant that its lost, right? that's what i was thought. let me get another crack at it with what you said. but i don't understand why u would have to set them equal together, since Q of water plus Q of metal alloy should equal 0 right?
 
  • #6
A positive number can never be equal to a negative number. So, what Dexter is doing is simply making sure they are both positive, and equating them.

If you want to strictly follow convention, you would swap Tf and Ti inside the brackets and then put a minus sign in front of one of the Q's. This will give the same result (the two minus signs will cancel out).
 

Related to How do I solve for the specific heat in a heat transfer problem?

What is specific heat and why is it important?

Specific heat is the amount of heat energy required to raise the temperature of one gram of a substance by one degree Celsius. It is important because it helps us understand how different materials respond to changes in temperature.

How is specific heat measured?

Specific heat is typically measured using a calorimeter, which is a device that measures the change in temperature of a substance when heat is added to it. The specific heat is then calculated by dividing the heat energy by the mass and temperature change.

What factors affect the specific heat of a substance?

The specific heat of a substance is affected by its molecular structure, density, and phase. Substances with more complex molecular structures tend to have higher specific heats, while substances with lower densities tend to have lower specific heats.

How does specific heat relate to heat capacity?

Specific heat and heat capacity are closely related. While specific heat is the amount of heat energy required to raise the temperature of one gram of a substance by one degree Celsius, heat capacity is the amount of heat energy required to raise the temperature of a specific amount (usually one mole) of a substance by one degree Celsius.

Why do different substances have different specific heats?

Different substances have different specific heats because of their varying molecular structures and densities. These differences affect how much energy is needed to raise the temperature of the substance, leading to variations in specific heat values.

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